doi:10.1016/j.cplett.2003.10.016 
Copyright © 2003 Elsevier B.V. All rights reserved.
Excited state dynamics of β-carotene explored with dispersed multi-pulse transient absorption
Faculty of Sciences, Vrije Universiteit Amsterdam, De Boelelaan 1081, 1081 HV, Amsterdam, The, Netherlands
Received 27 August 2003;
revised 2 October 2003.
Available online 4 November 2003.
References and further reading may be available for this article. To view references and further reading you must
purchase this article.
Abstract
The excited-state dynamics of β-carotene in hexane was studied with dispersed ultrafast transient absorption techniques. A new excited state is produced after blue-edge excitation. Pump–repump–probe and pump–dump–probe measurements identified and characterized this state, termed S‡, which exhibits a blue-shifted spectrum with a longer lifetime than S1. We establish the independent co-existence of the S‡ and S1 states following the relaxation of S2 and demonstrate that S‡ is an electronically excited state and not a vibrationally excited ground-state species. Our data support the premise that S‡ is formed directly from S2 and not via preferential excitation of ground-state sub-populations.
Fig. 1. Different multi-pulse processes observed in the β-carotene. For comparison, the one-photon absorption spectrum is displayed on the left of the figure. (A) 2P2PA process when the two pulses are temporally overlapped. (B) PrPP process with the S1 → Sn transition. (C) PDP process with the S2 → S0 transition. (D) PrPP process with the S2 → Sn transition. The Sn electronic states accessed in the PrPP and 2P2PA processes need not necessarily be the same due to symmetry considerations of the electronic states and the two-photon transition selection rules.
Fig. 2. Dual excitation PP transient signals. (a) Transient spectrum measured at 3 ps: 400-nm excitation (solid curve), 500-nm excitation (dashed curve) and the difference spectrum between the two (dot-dashed curve). The amplitude of the 500-nm spectrum is scaled (by 17%) to the 400-nm signal such that the bleach signals, at 450 nm, have equal magnitudes. (b) Normalized traces of the 500-nm excitation signals, measured at 510- (filled circles) and 550-nm (open circles). (c) Normalized traces of the 400-nm excitation signals measured at the same probe wavelengths. Same line demarcations as in panel b.
Fig. 3. PrPP spectra (800 nm). β-carotene was excited either at 400 or 500 nm and then interacted with 800-nm pulses. (a,b) Transient spectra measured with a probe time of 3 ps and a 800-nm delay at 1 ps. The PP spectrum (solid line), PP + 800-nm spectrum (dotted line) and 800-nm induced changes (dashed line). (c,d) Normalized PP spectra with the 800-nm induced changes. Same line demarcations as in panels a,b. Note that the ΔΔOD spectra are inverted and re-scaled.
Fig. 4. PrPP traces (800 nm). β-carotene was excited either at 400 or 500 nm and then interacted with 800-nm pulses. (a) 550-nm Kinetic trace measured with an 800-nm delay time of 300 fs. The PP trace (filled circles), PP + 800-nm spectrum (unfilled circles) and 800-nm induced changes (filled triangles). (b–d) Action traces excited and measured at different wavelengths (see labels) with the probe time at 3 ps.
Fig. 5. Experiment (530 nm). β-carotene was excited at 400 nm and then interacted with 530-nm pulses. (a,b) Kinetic trace measured at 550 and 580 nm, with the 530-nm pulse at 3 ps. The same line demarcations as in
Fig. 3a. (c) Action kinetics measured at 450 and 550 nm. (d) Normalized 3 ps PP spectrum (dotted line) and the negative Action-Spectra from global analysis: S
2 dump spectrum (300 fs), solid line, S
1 repump spectrum (10 ps), dashed line.
Abstract
Purchase PDF (357 K)
E-mail Article
Add to my Quick Links
Cited By in Scopus (44)
Purchase PDF (248 K)
, 
, Emmanouil Papagiannakis
